1. Technical Field
The present invention relates to an electromagnetic bandgap structure, more specifically to an electromagnetic bandgap structure and a printed circuit board having the same that prevent a signal ranging a predetermined frequency band from being transferred.
2. Description of the Related Art
New electronic apparatuses and communication apparatuses are increasingly becoming smaller, thinner and lighter, reflecting today's emphasis on growing mobility.
These electronic and communication apparatuses have various complex electronic circuits (i.e. analog circuits and digital circuits) for performing their functions and operations. These electronic circuits typically carry out their functions by being implemented in a printed circuit board (PCB). The electronic circuits on the PCB commonly have different operation frequencies from one another.
The printed circuit board in which various electronic circuit boards are implemented often has a noise (i.e. mixed signal) problem, caused by the transfer and interference of an electromagnetic (EM) wave resulted from the operation frequency and its corresponding harmonics components of one electronic circuit to another electronic circuit. The transferred noise can be roughly classified into radiation noise and conduction noise.
The radiation noise can be easily prevented by covering a protective cap on the electronic circuit. However, preventing the conduction noise is not as easy, because the conduction noise is transferred through a signal transfer path inside the board.
The noise problem will be described in more detail with reference to FIG. 1. FIG. 1 is a sectional view showing a printed circuit board including two electronic circuits having different operation frequencies. Although FIG. 1 shows a 4-layered printed circuit board 100, it shall be obvious that the printed circuit board can be modified to have a 2-, 6- or 8-layered structure.
As shown in FIG. 1, the printed circuit board 100 includes metal layers 110-1, 110-2, 110-3 and 110-4 (hereinafter, collectively referred to as 110) and dielectric layers 120-1, 120-2 and 120-3 (hereinafter, collectively referred to as 120) interposed between the metal layers 110. The top metal layer 110-1 of the printed circuit board 100 is equipped with two electronic circuits 130 and 140 having different operation frequencies (hereinafter, referred to as a first electronic circuit 130 and a second electronic circuit 140, respectively). In a mobile communication apparatus, for example, such as a mobile phone, the two electronic circuits 130 and 140 having different operation frequencies can be a digital circuit, functioning as a micro processor, and an RF circuit (i.e. analog circuit), for receiving and transmitting an RF signal.
Here, if it is assumed that the metal layer represented by reference numeral 110-2 is a ground layer and the metal layer represented by reference numeral 110-3 is a power layer, each ground pin of the first electronic circuit 130 and the second electronic circuit 140 is electrically connected to the metal layer represented by reference numeral 110-2, and each power pin is electrically connected to the metal layer represented by reference numeral 110-3. In the printed circuit board 100, every ground layer is also electrically connected to each other through vias. Similarly, every power layer is also electrically connected to each other through vias (refer to the reference numeral 160 in FIG. 1).
If the first electronic circuit 130 and the second electronic circuit 140 have different operation frequencies, a conductive noise 150 caused by an operation frequency of the first electronic circuit 130 and its harmonics components is transferred to the second electronic circuit 140, as shown in FIG. 1. This has a disadvantageous effect on the accurate function/operation of the second electronic circuit 140.
With the growing complexity of electronic apparatuses and higher operation frequencies of digital circuits, it is increasingly more difficult to solve this conduction noise problem. Especially, the typical bypass capacitor method or decoupling capacitor method for solving the conductive noise problem is no longer adequate, as the electronic apparatuses use a higher frequency band.
Moreover, the aforementioned solutions are not adequate when several active devices and passive devices need to be implemented in a complex wiring board having various types of electronic circuits formed on the same board or in a narrow area such as a system in package (SiP) or when a high frequency band is required for the operation frequency, as in a network board.